Geographic Information Systems (GIS) are computer systems used for storing, retrieving, analyzing, and displaying spatial data. Considering the spatial nature of many environmental and socio-economic impacts, GIS can be a very important tool in all impact assessment stages and may even act as an integrating framework for the whole impact assessment process. However, the widespread application of GIS in impact assessment still remains to be realized because of drawbacks such as the time and money necessary to invest in GIS, and the lack of data available in an appropriate form that can be loaded directly into the systems. This paper reviews case studies and key developments, and discusses several advantages and disadvantages of using GIS for impact assessment.